justyo

Yo (justyo.co) was a single-tap notification app and "the world's simplest API." A service registered an API username, received an api_token, and could push a lightweight "Yo" notification to a single subscriber or broadcast to all subscribers, optionally attaching a link, plus read the subscriber count. The Yo API had effectively one job — fire a push — with an api_token for auth (an OAuth 2.0 page was documented but never enabled) and first-party client SDKs across Python, PHP, Java, Node, Ruby, Scala and iOS under the github.com/YoApp organization. The Yo service is now defunct: the justyo.co host is suspended and its api/docs/dev subdomains no longer resolve. This API Evangelist profile captures the historical Yo API surface for the record.

justyo publishes 2 API contracts indexed on the APIs.io network: Account API and Yo API. Tagged areas include Company, Notification, Push Notifications, Messaging, and Mobile.

The justyo catalog on APIs.io includes 1 Spectral governance ruleset.

justyo’s developer surface includes documentation, signup flow, authentication, and 14 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

0.0/100 minimal ▬ flat Agent 0/100 human only Heartbeat 0/100 dormant saas Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

1 published contract 1 Agent Skills

Company Notification Push Notifications Messaging Mobile Developer Tools Defunct

Kin Score

Kin Score How this is scored →
scored 2026-11-06 · rubric v0.27.0

Composite quality — 0.0/100 · minimal

Contract Quality 0.0 / 19

Developer Ergonomics 0.0 / 15

Access Clarity 0.0 / 15

Operational Transparency 0.0 / 10

Contract Governance 0.0 / 9

Discoverability 0.0 / 8

Regulatory Posture 1.8 / 15

Create-or-Update Ergonomics 0.0 / 10

Agent readiness — 0/100 · human only

Machine-Readable Contract 18 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 8 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 7 / 7

Typed Event Surface 0 / 6

Agent Skills 5 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics applies to this provider. This API accepts writes, so it carries 10 points of the composite. It is scored from the published contracts themselves: whether a caller can create-or-update in one call, whether the write accepts a key the caller already holds, and whether the response says which branch ran. Without that, every write needs a search-and-branch in front of it, and the first time that check is skipped a duplicate record is created. Scored against the observed mean rather than raw — a provider at the catalog average is unchanged by this facet, not penalised by it.

The six quality facets above are damped to 75 points between them, because the conditional facet above carries the other 25. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 75% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

Show this score on your site.

It updates itself when the score changes. Paste this where you link to your API docs:

<a href="https://apis.io/providers/justyo/"><img src="https://apis.io/badge/justyo/card.svg" alt="justyo on APIs.io — Kin Score by API Evangelist"></a>

Other styles, a README pill and a shields.io endpoint are on the badge page.

Raise your score.

Agent readiness — checks not met, largest first (exact, from this profile):

MCP Server +12 pts — deployment.mode + probe verdict on the mcp/ manifest, not the pointer; an unprobed slug falls back to authorship
Agentic Access Contract +10 pts — agentic_access artifact present (x-agentic-access), graded by author
Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented)
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Request/Response Examples +7 pts — share of operations carrying request/response examples; else an Examples / Code Samples link
Registration Without a Human +6 pts — a `registration_endpoint` in the served RFC 8414 / OIDC discovery document

8 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Contract Quality scores 0.0 — up to +25.0 composite points
Developer Ergonomics scores 0.0 — up to +20.0 composite points
Access Clarity scores 0.0 — up to +20.0 composite points

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/justyo/apis.yml: open an issue on github.com/api-evangelist/justyo to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Markets this provider is in provisional

The Kin Score Market layer reads a provider inside its market: its position, and how deep its integrations go. Depth is only comparable within a position. Provisional and unweighted: not part of the Kin Score or agent readiness.

Market	Position	Depth	Registered MCP server	Declares compatibility
Mobile SDK Publishers (Play SDK Index, CocoaPods, ADA certification)	undeclared	-	-	-

Registered MCP server and declares compatibility are report only — not weighted. Undeclared means we found nothing we can read, so there is no number: we never infer integrations.

Standards implemented 1

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

OpenAPI

measured — observed by APIs.io (published)

APIs 2

Individual APIs this provider publishes, each with its own machine-readable definition.

justyo Account API

Read account/subscriber information.

justyo Yo API

Send Yo notifications to subscribers.

Open Collections 2

Open, tool-agnostic API collections (OpenAPI-derived and Bruno).

Yo Account API

OPEN COLLECTION

Account Yo API

OPEN COLLECTION

Agent Skills 1

Packaged agent skills for driving this provider's APIs from an AI assistant.

Send a Yo notification

AGENT SKILL

Rate Limits 1

Documented rate limits and quota policies.

Justyo Rate Limits

1 limits

RATE LIMITS

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs.

justyo API Rules

58 rules · 56 errors 1 warnings 1 info

SPECTRAL

OpenAPI Overlays 1

Overlays applied on top of this provider's contracts. Each card says who wrote it: a document the provider publishes, or one API Evangelist derived or generated.

Justyo Yo Overlay

2 actions · update · justyo-yo-openapi.yml

DERIVED

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Justyo Authentication

apiKey · 1 scheme

SECURITY

Justyo Domain Security

no transport/DNS hardening detected

SECURITY

Resources

Get Started 2

Portal, sign-up, and the first successful call

DeveloperPortal

DeveloperPortal

SignUp

SignUp

Documentation 1

Reference material describing how the API behaves

Documentation

Documentation

Agent Surfaces 4

MCP servers, agent skills, and machine-readable catalogs

X-MCPServerCandidate

LLMsTxt

WellKnown

AgentSkill

Design & Contract 2

Pagination, idempotency, versioning, errors, and events

Conventions

Conventions

Lifecycle

Lifecycle

Build 3

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

GitHubOrganization

Packages

Packages

SDKs

SDKs

Access & Security 2

Authentication, authorization, and security posture

Authentication

Authentication

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

RateLimits

RateLimits

Company 1

The organization behind the API

Website

Website

Other 1

Properties that don't map to a standard resource type

Overlay

Overlay

Source (apis.yml)

aid: justyo
name: justyo
description: 'Yo (justyo.co) was a single-tap notification app and "the world''s simplest API." A service registered an API
  username, received an api_token, and could push a lightweight "Yo" notification to a single subscriber or broadcast to all
  subscribers, optionally attaching a link, plus read the subscriber count. The Yo API had effectively one job — fire a push
  — with an api_token for auth (an OAuth 2.0 page was documented but never enabled) and first-party client SDKs across Python,
  PHP, Java, Node, Ruby, Scala and iOS under the github.com/YoApp organization. The Yo service is now defunct: the justyo.co
  host is suspended and its api/docs/dev subdomains no longer resolve. This API Evangelist profile captures the historical
  Yo API surface for the record.'
url: https://raw.githubusercontent.com/api-evangelist/justyo/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- slow-ventures
x-tier: stub
x-tier-reason: portfolio-lead
x-status: defunct
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: false
  label: Hosted service · you call their endpoint
  confidence: medium
  source:
  - openapi
  - pricing
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - authentication
  - rate-limits
  - security
  generated: '2026-11-06'
  method: derived
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-09-16'
image: https://raw.githubusercontent.com/api-evangelist/justyo/refs/heads/main/openapi/justyo-yo-openapi.yml
tags:
- Company
- Notification
- Push Notifications
- Messaging
- Mobile
- Developer Tools
- Defunct
tags_raw:
- Company
- Notifications
- Push Notifications
- Messaging
- Mobile
- Developer Tools
- API
- Defunct
apis:
- aid: justyo:justyo-account-api
  name: justyo Account API
  description: Read account/subscriber information.
  humanURL: https://docs.justyo.co/
  baseURL: https://api.justyo.co
  tags:
  - Account
  properties:
  - type: OpenAPI
    url: openapi/justyo-account-api-openapi.yml
  - type: Authentication
    url: authentication/justyo-authentication.yml
  - type: RateLimits
    url: rate-limits/justyo-rate-limits.yml
  - type: ErrorCatalog
    url: errors/justyo-problem-types.yml
  - type: DataModel
    url: data-model/justyo-data-model.yml
  - type: Conventions
    url: conventions/justyo-conventions.yml
- aid: justyo:justyo-yo-api
  name: justyo Yo API
  description: Send Yo notifications to subscribers.
  humanURL: https://docs.justyo.co/
  baseURL: https://api.justyo.co
  tags:
  - Yo
  properties:
  - type: OpenAPI
    url: openapi/justyo-yo-api-openapi.yml
  - type: Authentication
    url: authentication/justyo-authentication.yml
  - type: RateLimits
    url: rate-limits/justyo-rate-limits.yml
  - type: ErrorCatalog
    url: errors/justyo-problem-types.yml
  - type: DataModel
    url: data-model/justyo-data-model.yml
  - type: Conventions
    url: conventions/justyo-conventions.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: RateLimits
  url: rate-limits/justyo-rate-limits.yml
- type: Overlay
  url: overlays/justyo-yo-overlay.yaml
- type: Website
  url: https://justyo.co
- type: Documentation
  url: https://docs.justyo.co/
- type: DeveloperPortal
  url: http://dev.justyo.co/
- type: GitHubOrganization
  url: https://github.com/YoApp
- type: SignUp
  url: https://dashboard.justyo.co/
- type: Packages
  url: packages/justyo-packages.yml
- type: SDKs
  url: packages/justyo-packages.yml
- type: X-MCPServerCandidate
  url: mcp/justyo-mcp.yml
  note: 'Renamed from MCPServer 2026-09-03 (roadmap#247): the manifest self-describes as status: candidate — a tool list derived
    from the published API contracts, not an existing server. The scorer already read the manifest and reported mcp_server
    correctly; the MCPServer type was crediting the artifact-type surfaces with a server that does not exist.'
- type: LLMsTxt
  url: llms/justyo-llms.txt
- type: WellKnown
  url: well-known/justyo-well-known.yml
- type: Authentication
  url: authentication/justyo-authentication.yml
- type: Conventions
  url: conventions/justyo-conventions.yml
- type: Lifecycle
  url: lifecycle/justyo-lifecycle.yml
- type: DomainSecurity
  url: security/justyo-domain-security.yml
- type: AgentSkill
  url: skills/_index.yml
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence

justyo API — frequently asked questions

Does justyo have an API?

Yes. APIs.io lists 2 APIs from justyo, including justyo Account API and justyo Yo API.

Is there an OpenAPI specification for the justyo API?

Yes. APIs.io indexes 2 OpenAPI specifications for justyo, each linked for download from this page.

How do I authenticate with the justyo API?

justyo uses bearer-token authentication (apiKey · 1 scheme). The details are profiled on APIs.io as Justyo Authentication.

Is the justyo API ready for AI agents?

justyo has a Kin Score of 0.0 out of 100 (minimal) and an Agent Readiness score of 0.0 (human-only), scored by API Evangelist on 2026-11-06.

Work with this as data

Every provider here is available over the APIs.io API and to AI agents over MCP.

MCP server

One button, every client — Claude, Cursor, VS Code and the rest.

https://apis.io/mcp

Tools for providers

9 MCP tools reach this

find_providersBrowse and filter every provider in the catalog.
get_provider_artifactsEvery artifact this provider publishes, grouped by type.
get_provider_operationsEvery operation across all of their OpenAPIs — one call instead of parsing every spec.
get_provider_toolsEvery MCP tool they ship, with the operation each wraps.
get_provider_evidenceHow each part of their score was established. Free — the basis for a claim should not sit behind it.
get_provider_ratingPRO — composite, band, trend and facet scores.
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.

All 92 tools →

Call it yourself

curl for this page

This provider

curl "https://apis.io/api/v1/providers/justyo"

All providers

curl "https://apis.io/api/v1/providers?limit=25"

Every operation they expose

curl "https://apis.io/api/v1/providers/justyo/operations?limit=25"

How their score was established

curl "https://apis.io/api/v1/providers/justyo/evidence"

Calls without X-API-Key need no key. Calls with it need a paid plan — get a key.

Get an API key

Free tier, no form to fill in. Signing in shares your email address with us — we store it to create your key and to recognise you if you sign in with another provider. See our Privacy Policy and Terms.

GitHub Google LinkedIn

A second provider on the same verified email joins the account you already have.